This invention relates to a fuel injection unit for an engine and method of operating such a fuel injection unit so as to reduce speed variations of the engine output shaft and a method of controlling the timing of an event in an internal combustion engine.
It is well known in multiple cylinder engines that different combustion characteristics from cylinder to cylinder can cause speed variations during the rotation of the output shaft angle as each cylinder fires. Noise, vibration and reduced output can result from such uneven speeds. Although it has been proposed to avoid cylinder to cylinder variation by mechanical adjustment, these mechanically adjusted devices are difficult to adjust and can not accommodate changes that may occur during the running of the engine. To avoid these problems, therefore, a system has been proposed wherein the speed increment added by each cylinder's firing is sensed and the amount of fuel supplied to each individual cylinder is varied so as to minimize variations in output shaft speed. Such a system is disclosed in the copending application entitled High Pressure Fuel Injection Unit, Ser. No. 656,244, filed Feb. 15, 1991 in the names of Jun Taue and Hidenori Suhara, which application is assigned to the Assignee hereof.
Although the system described in the aforenoted co-pending application is extremely effective, it is quite complicated in that it is necessary to measure the speed contributed by each cylinder and control each cylinder individually.
It is, therefore, a principal object of this invention to provide an improved fuel injection unit for an engine and method of operating it in which speed variations are substantially reduced or eliminated.
It is a further object of this invention to provide an improved and simplified arrangement for controlling uneven firing impulses generated by individual cylinders of a multiple cylinder fuel injected engine.
In connection with controlling the timing of the fuel injection of an engine or, for that matter, other events occuring in the engine such as the firing of a spark plug, it is a normal practice to employ a toothed wheel that rotates in unison with the engine output shaft and which has a plurality of teeth for providing individual pulses that indicate the angular position of the engine output shaft. However, it is not practical to employ a number of teeth equal to each degree or fractional degree of rotation of the crankshaft. Therefore, the timing of the events of the engine may not necessarily coincide with the individual pulses of the toothed timing wheel. Therefore, it is necessary to make some computation of the time it takes for the engine output shaft to rotate from one tooth until the occurrence of the event which is to be timed.
In order to calculate the time period between the toothed wheel pulse and the time which the event is to occur, it is necessary to measure the speed of rotation of the output shaft. This is normally done by selecting the time it takes the output shaft to rotate through a given angle and this is done by measuring the time at takes for a number of teeth on the toothed wheel to pass a sensor.
As has been noted, however, the speed of the output shaft varies during a single rotation and hence it is important to insure that the calculated speed is close to the speed which actually exists at the time the event is to occur. However, if a fixed number of teeth on the wheel at a fixed location are chosen, this may not coincide with the speed of rotation at the time immediately preceding the event to be timed.
It is, therefore, a further object of this invention to provide an improved method for measuring the speed of an output shaft at a time as close as possible to the occurrence of the event to be timed.
It is a further object of this invention to provide an improved method for measuring the speed of the output shaft of an engine to time an event.
In conjunction with the control of the initiation and duration of fuel injection by individual fuel injectors, it has been the practice to provide a sensing mechanism that senses the output shaft angle of the engine and also the rotational speed of the engine. Of course, this means that the fuel injection system must cooperate with sensors that are mounted on the engine independently of the fuel injector. This can give rise to some difference in the phase angle between the output shaft of the engine and the shaft of the fuel injection pump. Although it has been proposed to incorporate an internal timer in the fuel injection pump, the internal timers previously proposed only measure the angular rotation of the pump shaft and do not sense the initiation or reference signal of the engine output shaft from which to base the timing calculations.
It is, therefore, a further object of this invention to provide a fuel injection pump for an engine wherein the timer for the operating sequence and duration thereof is self contained within the fuel injection pump.